Thomson And Resonant Scattering In The X-ray Spectrum Of The Recurrent Nova U Sco

Type Conference Paper
Names Marina Orio, T. Nelson, J. Gallagher
Proceedings Title Bulletin of the American Astronomical Society
Conference Name American Astronomical Society, HEAD Meeting #12, #11.06
Volume 12
Date September 1, 2011
URL http://adsabs.harvard.edu/abs/2011HEAD...12.1106O
Library Catalog NASA ADS
Abstract We report the results of a Chandra observations with the HRC-S detector and the LETG grating of the recurrent nova U Scorpii S 17 days after the observed visual maximum of 2010, and compare them with XMM-Newton observations done 22 and 34 days after maximum. The X-ray high resolution spectra evolved very quickly, following pattern seen before only in the optical spectra of novae. On day 17 we observed composite spectrum in which about 70% of the flux was in the continuum and 30% was emitted in broad, red-shifted emission line components of P-Cyg lines of nitrogen. Five days later the absorption components disappeared and only broad and asymmetric emission lines were detected. On day 34, the lines had a triangular profile and the peak moved closer to zero velocity. The strongest lines were always due to resonant transitions. Emission lines due increasingly higher ionization states gradually appeared. />The total absorbed flux increased from 2.7 x 10(-11) erg/cm/s in February to 3.4x 10(-11) erg/cm/s in March, with corresponding unabsorbed luminosity in the range 0.8--1.8 10(37)/(12 kpc) Although we can fit the continuum with a white dwarf (WD) atmosphere model, we could not measure the absorption lines, embedded in the broad lines (with P-Cyg and later with just emission profiles produced in the nova wind. However, we derive the ranges for the atmospheric temperature, 500,000-730,000 K in the first observation, and 700,000 K to a million K in the last observation, done at the peak of the X-ray light curve observed with Swift. The peak temperatur eis consistent with a WD mass above 1.2 m(sol. A deep X-ray eclispe with the same period ss the optical eclipse is attributed to the Thomson scattered continuum of the WD radiation, rather than to direct observation of the WD.
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